4 stroke diesel engine - practical PDF

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Four stroke diesel engine Apparatus: Four stroke diesel engine A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction.

Four stroke diesel engine works on diesel cycle and it consists of four strokes namely suction, compression, expansion and exhaust. ... In compression stroke, the charge that is in cylinder is compressed and at the end of this stroke fuel is injected, which leads to combustion of fuel and further expansion stroke occurs. Diesel engine, also known as compression ignition (C.I.) engine is widely used in automobile industries. Big vehicles such as truck, bus, locomotive engine etc. used diesel engine as the power unit because of its higher torque and greater mileage than petrol engine. The ignition temperature of diesel is lower than petrol so the working of diesel engine is slightly different than petrol engine.

 Parts of four stroke petrol engine: The parts of four stroke petrol engine are given below

 Piston : A piston is a component of reciprocating engines. It is located in a cylinder and is made gas-tight by the piston rings. Its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod or connecting rod.

 Propelling Nozzeel : For jet engines forms of internal combustion engines, a propelling nozel is present. This takes the high temperature, high pressure exhaust and expands and cools it. The exhaust leaves the nozzel going at much higher speed and provides thrust, as well as costricting the flow from the engine and raising the pressure in the rest of the engines, giving great thrust for the exhaust mass that exists.

 Crankshaft : Most resiprocating internal combustion engines end up turning a shaft. This means that the linear motion of a piston must be converted into rotation. This is typically achieved by a crankshaft.

 Flywheels : The flywheel is a disk wheel attached to the crank, forming an internal mass that stores rotational energy. In engines with only a single cylinder the flywheel is esential to carry the energy over the power stroke into a subsequent compression stroke. Flywheels are present in most resiprocating engines to smooth out the power delivery over each rotation of the crank and in most automotive engines also mount a gear ring for a starter.

 Connecting Rod:

It connect piston to the crankshaft and transmit the motion of the piston to crankshaft. The lower end is connected to piston and the upper end to cranksha

 Valves : All four-stroke internal combustion engines employ valves to control the admittance of fuel and air into the combustion chamber.

 Fuel injector: A fuel injector is used in the diesel engine to inject fuel into the system which causes combustion.

 Working of a four stroke Diesel engine: Power generation in four stroke is divided into four parts namely suction stroke, compression stroke, expansion stroke (power stroke) and exhaust stroke.

 Suction stroke: In the suction stroke of diesel engine the piston start moves from Top Dead Centre (TDC) of the cylinder to Bottom Dead Centre (BDC) of the cylinder and simultaneously inlet valve opens. At this time air at atmospheric pressure drawn inside the cylinder through the inlet valve due to the suction created.

The inlet valve remains open until the piston reaches the BDC of cylinder (not practically but theoretically.

 Compression stroke: After the piston passes BDC of the cylinder, it starts moving up. Both valves are closed and hence the cylinder is sealed. The piston moves upward. This movement of piston compresses the air into a small space between the piston and TDC of cylinder . The air is compressed into 1/22 (compression ratio: 22, varies from engine to engine) or less of its original volume. Due to this compression a high pressure and temperature is generated inside the cylinder. Both the inlet and exhaust valves do not open during any part of this stroke. At the end of compression stroke the piston is at TDC the cylinder.

 Power stroke: At the end of the compression stroke when the piston is at TDC a pre metered quantity of diesel is injected into the cylinder by the injector. The temperature inside the cylinder is very high which is sufficient to ignite the fuel injected and this generates tremendous energy which is in the form of high pressure which pushes down the piston. The connection rod carries this force to the crankshaft which turns to move the vehicle. At the end of power stroke the piston reaches the BDC.

 Exhaust stroke: When the piston reaches the BDC after the power stroke, the exhaust valve opens. The pressure of the burnt gases is higher than atmospheric pressure. This pressure difference allows burnt gases to escape through the exhaust port and the piston move through the TDC. At the end of exhaust all burn gases escape (theoretically) and exhaust valve is closed.

The cycle repeats.

 Advantages of four stroke petrol engine : 

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More torque : In general 4 stroke engine always make extra torque than 2 stroke engine at low RPM but it has lot to do with fuel efficiency. More fuel efficiency : 4 stroke engines have greater fuel efficiency than 2 stroke because fuel is consumed once every 4 strokes. Less pollution : As power is generated once every four strokes and also as no oil or lubricant is added to the fuel, 4 stroke engine produces less pollution. More durability : We all know that more the engine runs, quicker it wears out a four stroke engine with 1oo rpm will runs for 100 minutes than the other two stroke engine. No extra additio0n of oil : Only the moving parts need lubrication intermediately. No extra oil or lubricant is added to fuel.

 Disadvantages of four stroke petrol engine : 

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Complicated design : A 4 stroke engine has a complex valve mechanism operated and controlled by gears and chain. Also there are many parts which makes it harder to troubleshoot. Less powerful : As power is delivered once every 2 rotations of crankshaft hence 4 stroke is less powerful. Expensive : A 4 stroke engine has much more parts then the 2 stroke engine. So it is expensive....